2 NOVEL PARTIAL DELETIONS OF LDL-RECEPTOR GENE IN ITALIAN PATIENTS WITH FAMILIAL HYPERCHOLESTEROLEMIA (FHSIRACUSA AND FHREGGIO EMILIA)

In the present study we report two novel partial deletions of the LDL- R gene. The first (FHsiracusa), found in an FH-heterozygote, consists of a 20 kb deletion spanning from the 5' flanking region to the intron 2 of the LDL-receptor gene. The elimination of the promoter and the f irst two exons prevents the transcription of the deleted allele, as sh own by Northern blot analysis of LDL-R mRNA isolated from the proband' s fibroblasts. The second deletion (FHReggio Emilia), which eliminates 11 nucleotides of exon 10, was also found in an FH heterozygote. The characterization of this deletion was made possible by a combination o f techniques such as single strand conformation polymorphism (SSCP) an alysis, direct sequence of exon 10 and cloning of the normal and delet ed exon 10 from the proband's DNA. The 11 nt deletion occurs in a regi on of exon 10 which contains three triplets (CTG) and two four-nucleot ides (CTGG) direct repeats. This structural feature might render this region more susceptible to a slipped mispairing during DNA duplication . Since this deletion causes a shift of the BamHI site at the 5' end o f exon 10, a method has been devised for its rapid screening which is based on the PCR amplification of exon 10 followed by BamHI digestion. FHReggio Emilia deletion produces a shift in the reading frame downst ream from Lys(458), leading to a sequence of 51 novel amino acids befo re the occurrence of a premature stop codon (truncated receptor). Howe ver, since RT-PCR failed to demonstrate the presence of the mutant LDL -R mRNA in proband fibroblasts, it is likely that the amount of trunca ted receptor produced in these cells is negligible.